This invention relates to display devices which include a face plate having arrays of openings therein which are arranged to form numerals, letters, or other indicia when light is transmitted through predetermined openings, and having a plurality of back plates movably mounted behind the face plate, each back plate having an array of light passages therein which are arranged to coact with the corresponding face plate openings to form the corresponding indicia. One example of a prior art display device of this general type is disclosed in U.S. Pat. No. 3,401,280. The above-noted patent discloses a digital clock having three back plates which are driven in an orbital path by an orbital drive mechanism. In practice, the above-described prior art orbital drive mechanism has been found to have a tendency to stick, with the possibility of stopping the clock.
Ballerini U.S. Pat. No. 1,594,703 and Hildburgh U.S. Pat. No. 1,172,360 disclose display devices having linear movement. In Ballerini there is a limit to the number of message changes which is possible and in Hildburgh a multiplicity of movable panels, one behind the other, is required.
One important object of this invention is to provide an improved back plate drive mechanism which is not subject to sticking.
Another important object of this invention is to replace the prior art orbital drive mechanism with a simpler, sturdier linear drive mechanism and to provide a device in which a relatively large number of indicia changes in possible with only one movable back plate.
Other objects, advantages, and features of the invention will be apparent from the disclosure hereof.